Device for preventing foaming of oil

ABSTRACT

A foam-preventing device for automobile hydraulic power units, comprising an intermediate pressure chamber located between an oil tank of the unit and the outlet of a flow-rate control valve of the unit for by-passing excess oil to the oil tank. Excess oil is forced by this arrangement to flow through the intermediate chamber so as to avoid a sudden pressure change and foaming thereof.

United States Patent- 191 lnventor: Akaike, Aikawa-Machi, Japan Assignee: Atsugi Motor Parts C0.,Ltd., Atsugi Foreign Application Priority "A r.26,1972 Japan... 47-4929quj u.s. c1 137/490, 137/255, 417/307 1n1.c1. G05d 16/00 Field of Search -137/488,' 492,5,-492,,538,

References Cited UNITED STATES PATENTS 2/1954 Ku piecm.

Akaike 1 June 4, 1974 [54] DEVICE FOR PREVENTING FOAMING OF 2,870,781 1/1959 Tennis 137/490 OIL 2,984,187 5/1961 Prasse et a1... 417/311 x 3,205,7 9 9/1965 Mandelko 188/269 )1 Primary Examiner1-lenry T. Klinksiek Assistant Examinr Robert .1. Miller Attorney, Agent, 0r Firr n--Er ic H. Waters 1571 l 1 ABSTIRVACTQ A foa'rn-preventing device for automobile hydraulic power] units, comprising an intermediate pressure chamber located between an oil tank of the unit and the outlet of a flow-rate control valve of the unit for by-passing excess oil tothe oil tank. Excess oil is forced by this arrangement-to flow through the intermediate chamber so as to avoid a sudden pressure changeand foaming thereof.

5 Claims, 5 Drawing Figures sum 2 OF 5 DEVICE FOR PREVENTING F GAMING OF OIL BACKGROUND OF THE INVENTION 1. Field of the Invention SUMMARY OF THE INVENTION The inventor has found through experiments that foams of hydraulic power unit oil, which are produced This invention relatesto a device for preventing pres- 5 at the time of releasing-its excess pressu can e resure oil from foaming in the bypass passage of an automobile hydraulic power unit.

2. Description of the Prior Art Modern automobiles are equipped with a hydraulic power unit for automatic operations, such as power steering, automatic gear changing, window wiper and- /or automaticdoor operation. To providing pressurized oil to the hydraulic power unit, anoil pump, usually a vane pump, is driven by using part 'of the output from the automobile driving engine. The revolving speed of the engine, e.g.,'an internal combustion engine, varies depending on the automobile speed, for instance, from Y 500 to 7,000 rpm (revolutions per minute). Since the discharge from the vane pump increases in proportion to its revolving speed, the amount of oil delivered from the vane pump to the hydraulic power unit varies in response to the variation of the automobile engine speed.

moved almost completely by applying a pressure (gauge pressure) of not smaller than 0.5 Kg/cm to the foamed oil.

Based on such finding, the present invention uses an 0 intermediate pressure chamber between the outlet of an oil pump, supplying pressure oil to the hydraulic .power unit, and an oil tank surrounding the oil pump,

which chamber has an orifice communicating with the oil tank so-as to release the discharge from the oil pump to the oil'tank through the chamber.

Asa result, the foaming of that portion of the discharge, which is to be released or by-passed through a flow-rate control valve, is completely eliminated by reducing the pressure of the bypass oil in two steps, i.e.,

to the pressure of the intermediate chamber and then to the atmospheric pressure, rather than directly to the atmospheric pressure 'in one step.

BRIEF DESCRIPTION OF THE DRAWING For a better'un'derstanding of the invention, reference is made to the accompanying drawing, in which:

FIG. 1 is a sectional view of a' hydraulic power unit for-automobiles, according to the present-invention; FIG.2 is'a front view of the hydraulic power unit;

FIG. 3 is a partially cut away front view of the hydraulic power unit; t FIG. 4 is a sectional view taken along the line IVIV of'FIG. 3; and

To this end, the surplus oil is passed to an oil tank through a by-pass type flow-rate control valve, for ensuring the constant oil flow to the members being controlled, regardless of the revolving speed of the automobile-driving engine.

With a conventional hydraulic power unit, the excess ing in the oildue to the expansion of air dissolved f therein. v

The foaming of the oil is accompanied with unpleasant noise, which is referred to as relief noise". The relief noise is particularly annoying when the vane pump is driven at a high speed without ha'ving'any load to the hydraulic power unit, because sustantially the entire discharge from the vane pump is released "through the narrow gap of the flow-rate control valve under such conditions. Besides, if foamed oilis drawn into the vane pump from the oil tank, it tends to disturb the lubrication of the pump and to cause cavitation which may lead to accelerated wearing of the pump.

Therefore, an object of the present invention is to obviate the aforesaid difficulties of the conventional hydraulic power units.

FIG. 5- is a sectionalview similar to FIG. 4, illustrating the open position of a flow-rate control valve.

Like parts are designated by like numerals throughout the different'figures of the drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT end of the rotary shaft 3, so that driving power applied to the pulley 4 is transmitted to the oil pump 5 through the shaft 3. The oil pump 5 may be a vane pump, and in such a case, a rotor (not shown) of the vane pump is connected to the inner end of the rotary shaft 3. The pulley 4 may be driven by a part of the output from automobile-driving engine (not shown).

The oil pump 5 has an inlet port 6 and adischarge port 7. An oil-tight cover 8 encloses the oil pump 5, with a spacing therefrom. The cover 8 is secured to the body 2 while inserting an oil-tight packing 9 therebetween,

, as shown in FIG. 1. Thus, an oil tank 10 is formed by using the spacing between the oil pump 5 and the cover 8. The cover 8 has an oil inlet opening 1 l, which is normatters from oil being supplied to the hydraulic power unit.

passage 14 of the boss 15.

3 The oil pump 5 has a hollow boss defining a passage 14 communicating with the outlet port .7 of the pump. The left-hand end of the boss 15, as seen inFIG. l, engages the cover 8, and an annular oil-tight packing 16 is inserted between the edge surface of the boss 15 and-the cover 8. The passage-l4 of the boss 15 communicates with a corresponding hole passing through the The nipple 17 has an orifice 17a formed at the end facing the outlet port7'of the'pum'p 5. Pressure o'il delivered to the loads (not shown) of the hydraulic power unit through an orifice 17a returns to theoil tank 10 at a return path coupling 20 which is sealingly secured to the cover 8. The coupling 20 has a strainer 21 which'is disposed within the oil tank 10.

Excess pressure-oil at the outlet port 7 of the pump 5 is by-passed to the oil tank 10 through a flow-rate control valve 40, which includes a cylindrical valve hole 23- bored in the boss 15, so as to extend in parallel with the passage l4'thereof, as shown in FIGS. 3 to 5. The lower end of the passage 14, as seen in F I05, 3 and 4, communicates with the corresponding lower end of the valve hole 23 through a port 22. The opening of the port 22 at the valve hole 23 is comparatively wide and extends nearly through a semi-circle about-the longitudinal central axis of the valve hole 23. A piston valve is slidably fitted in the cylindrical valve hole 23, so as to selectively communicate thev port 22 with an annular groove 28 bored on the peripheral surface of the valve hole 23 with a short distance from the port 22, as shown in FIGS. 4 and 5. The piston valve 25 is biased by a coiled spring 24 in a direction to interrupt the communication between the port 22 and the annular groove 28. The piston valve 25 has a stopper 27 which limits the movement of the piston valve 25, Another annular oil-tight packing 26is disposed between the boss 15 and the body 2, for preventing the leakage of the pressure oil through the boundary therebetween.

The piston valve 25 has an axialhole 31, which extends coaxially with the longitudinal central axis of the piston valve 25 and has an open endat the back of the piston valve 25. Lateral holes 32 extend at right angles to the longitudinal axial center-line of the piston valve, so as to communicate the axial hole 31 with the port 29 toward the chamber 30 at the lower end of the hole 31, as shown in FIGS. 4 and 5. After placing a valve holder carrying a spherical valve 34 and a coiled spring 36 in the axial hole 31, a valve seat 33 is screwed in the open top end of the axial hole 31. The coiled spring 36 acts to normally urge the valve holder 35 upwards so as to'keep a central passage of the valve seat 33 as blocked or closedby the spherical valve 34.

the nipple 17 at the downstream of the orifice 17a.

such communication between the valve hole 23 and the nipple 17 is provided by a passage 37 formed through 'the'wall of the valve hole 23 and a radial hole 38 bored through the wall of the nipple 17, as shown in FIGSQ4 and 5.

In operation, the pressure difference between theline pressure at the downstream of the orifice 17a of the nipple 17 and the discharge pressure of the oil pump 5 at the discharge port 7 is a applied across the piston valve 25. Thus, as the discharge from the oil pump 5 increases, the pressure acting on the lower surface of the piston valve 25 increases, so as to raise the valve 25 for widening the passage from the lower portion of the valve hole 23 to the annular groove 28, as shown in FIG. 5. As a result, the amount of by-pass oil toward the intermediate pressure chamber 30 increases. .The oil delivered to the intermediate pressure chamber 30 is gradually released to the oil tank 10 through the orifice 30a. Accordingly, as the discharge pressure from the oil pump 5 is-raised, the amount of the pressure oil discharged to the oil tank 10 increases, so as to keep the .line pressure downstream of the orifice 17a substantially at a desired constant level.

It is apparent that, as the discharge from the oil pump 5 is decreased,.the pressure acting on the lower surface Another port 29 communicates the annular groove 28 on the peripheral surface of the valve hole 23 to an intermediate pressure chamber 30, which is a cylindrical hole bored-through the boss 15 in parallel to the passage 14 and the valve hole 23, as shown in FIGS. 3 to 5. Thus, the lower end portionof the intermediate pressure chamber 30, as seen in FIGS. 4 and 5, has a bottom wall and communicates with the valve hole 23, while the upper portion of the chamber 30 communicates with the oil tank 10 through an orifice 30a formed at the wall of the intermediate pressure chamber 30 with a small distance from the open top of the chamber 30.

In the embodiment of FIGS. 4 and 5, a stay bolt 39 extends through the intermediate pressure chamber 30, so as to securely hold the cover 8 and the mounting bracket 18 against the open top ofthe chamber 30 for closing it. Such stay bolt 39 is not essential in the present invention, andit may be dispensed with if the open top of the chamber 30 is properly closed by the nipple 17 and associated fastening means.

of the piston valve 25 is reduced to allow the piston valve 25 to move downwards for restricting the amount of the pressure oil being by-passed from the oil pump discharge port 7 to the intermediate pressure chamber 30, Thus, the line pressure downstream of the orifice 17a is kept substantially at the desired constant level.

If the line pressure suddenly increases, due to one reason or other, the spherical valve 34 is pushed downwards for allowing the oil in the upper portion of the valve hole 23 to escape into the intermediate pressure chamber 30 through the central passage of the valve seat 33, the axial hole 31 of the piston valve 25, and the transverse holes 32 thereof. As a result, the pressure acting on the upper surface of the piston valve 25 is reduced to allow the piston valve 25 to move upwards for 4 narrow gap between the piston valve 25 and the annular groove 28, As a result, considerable foaming is caused in the oil of the oil tank 10, while generating annoying relief noise.

With the present invention, the oil being by-passed is not directly released to the oil tank 10, but it is once introduced to the lower portion of the intermediate pressure chamber 30, and then allowed to proceed into the oil tank through the orifice 30a at the upper portion of the chamber 30. Thereby, the foaming of theoil and the relief noise are completely eliminated. The inventor has found that favorable results can be obtained when the differential pressure across the orifice 30a, i.e., between the intermediate pressure chamber 30 and the oil tank 10, is 0.5 Kg/cm to 3 Kglcm If the orifice 30a is too large, the differential pressure across it cannot be maintained in the aforesaid range, so that the desired function of the intermediate pressure chamber cannot be achieved. On the other hand, if the orifice 30a is too small, resistance-to the by-pass flow of the oil becomes excessively high, and the desired flow-rate control characteristic and the desired constant line-pressure characteristic cannot be obtained. 7

As described in the foregoing disclosure, according to the present invention, ,there is provided a foampreventing device to be used in a hydraulic power unit in cooperation with a by-pass type flow-rate control valve, for keeping a constant line pressure regardless of the revolving speed and discharge pressure of an oil pump. The'foam-preventing device also eliminates relief noise by prohibiting the by-pass oil from foaming.

Furthermore, the foam-preventing device of the present invention is effective in eliminating detrimental effects of foamed oil on the lubrication of an oil pump,

whereby a long service life of the oil pump can be ensured. V i

What is claimed is: r

1. A device forpreventing foaming of oil being bypassed in an automobile hydraulic power unit which latter includes a by-pass type flow-rate control valve which selectively by-passes part of the discharge from an oil pump into an oil tank so as to ensure desired oil flow toward loads of the unit, the device comprising an intermediate pressure chamber communicating with the outlet of said control valve through one port and having one orifice formed through a wall of said pressure chamber which faces said oil tank, whereby the entirety of the discharge part from said oil pump is guided to flow toward said oil tank through said orifice of the pressure chamber, the pressure of the discharge being regulated at a level between that at the discharge from said oil pump and that in said oil tank.

2. The device as defined in claim 1, wherein the differential pressure-across said orifice of the pressure chamber is 0.5 t Q3Kg/crn i 3. The device as defined in claim 1, wherein said ber. 

1. A device for preventing foaming of oil being by-passed in an automobile hydraulic power unit which latter includes a by-pass type flow-rate control valve which selectively by-passes part of the discharge from an oil pump into an oil tank so as to ensure desired oil flow toward loads of the unit, the device comprising an intermediate pressure chamber communicating with the outlet of said control valve through one port and having one orifice formed through a wall of said pressure chamber which faces said oil tank, whereby the entirety of the discharge part from said oil pump is guided to flow toward said oil tank through said orifice of the pressure chamber, the pressure of the discharge being regulated at a level between that at the discharge from said oil pump and that in said oil tank.
 2. The device as defined in claim 1, wherein the differential pressure across said orifice of the pressure chamber is 0.5 to 3Kg/cm2.
 3. The device as defined in claim 1, wherein said pressure chamber is an elongated cylindrical chamber disposed adjacent said control valve.
 4. The device as defined in claim 3, wherein said pressure chamber receives the by-pass oil from said control valve at one longitudinal end thereof while delivering the by-pass oil to said oil tank at the opposite longitudinal end thereof.
 5. The device as defined in claim 3, further comprising a stay bolt for said cylindrical pressure chamber, extending along the longitudinal center line thereof, for holding members close to at least one end of said chamber. 